That article from The National Interest by Colin P. Clarke and Phillip Smyth and thanks to both. Read the whole article.

"In early December, senior Trump administration officials suggested that approximately 80 percent of Syrian leader Bashar al-Assad’s defense against insurgents in the country’s ongoing civil war is being provided by forces imported from outside of the country. The lion’s share of these fighters is being trained and equipped by Iran, the Assad regime’s most ardent supporter."

That "lion's share" as described close to 84 %! Outsiders Muslims of the Shia persuasion, outcasts and pariahs to a large extent.in their homelands gainfully employed perhaps even grateful for the opportunity both to make some money and support and die for the faith.